Composite materials are generally stronger, lighter and more resistant to high temperatures compared to steel. In general, composite materials also can be more readily formed into irregular shapes and configurations. For these reasons, composite materials are competitive with, if not replacing, steel and other materials in the manufacture of items from tennis racquets, golf clubs, and bicycle frames, to parts for automobiles, aircraft and even spacecraft.
Composite materials are typically made of two general components: a reinforcing material that provides the properties of strength and stiffness, and a binding material or matrix which acts like glue holding the reinforcing material in place. Composite materials have characteristics superior to those inherent in the reinforcing or binding materials alone.
A well known example of synthetic composite material is graphite composite. Graphite composite materials generally consist of carbon fibers, which act as the reinforcing material, held in place by binding material such as an epoxy or polymer matrix resin. The carbon fibers can be woven into cloth, braided into tubes, etc., before they are coated or impregnated with the resin matrix. After the carbon fibers are impregnated with resin, this pliable “wet layup” is applied to a mold before the resin matrix is allowed to cure. Depending on the type of resin or matrix used, curing might occur at room temperature or it might require elevated temperatures. The curing of the resin matrix causes the composite material to harden. Once the part is cured, the part is removed from the mold and any additional finishing or cleanup operations can be performed. Regardless of the manufacturing techniques or the types of reinforcing and binding materials involved, molds are typically used to define the shape of the fabricated composite component.
The molds used in composite fabrication can be either male or female. Female molds most directly effect the exterior surface of a produced component, and male molds most directly effect the interior surface of a produced component. A matched mold (male and female) is required if the part is consolidated using a press. The molds can be made from materials such as composite materials (including elastomeric materials) or metal filled epoxy, or they can be machined from aluminum or steel. Molds can also be solid or formed by inflatable structures such as bladders. The type of mold and materials used may depend on the type of part and the production quantity.
In the case of inflatable elastomeric bladders used in composite fabrication, a vent component must be attached to the bladder material in a manner that forms an airtight seal so that the vent is able to control gas flow during inflation and deflation, as well as maintain internal pressures within the bladder during the layup and curing process. Typically the vent component is bonded to the elastomeric material of the bladder using chemical adhesives. However, as discussed below the use of chemical adhesives to create an airtight bond between the bladder material and the vent component presents a number of challenges.
Adhesive bonding is a time consuming and temperamental process. Improper application of the chemical adhesive can compromise the airtight bond required to be formed between the vent component and the inflatable bladder. Some parameters that can cause a failure of the bond's ability to eliminate unwanted gas flow include quantity of adhesive applied, evenness of adhesive application, orientation of the elastomeric material of the inflatable bladder relative to the adhesive and the surface of the vent component to which the bladder is to be bonded, pressure applied to the bonding components, and curing times. For example, the presence of air bubbles in the chemical adhesive weakens the bond. Moreover, if too many air bubbles are present, the bubbles can collectively create a path for unwanted airflow causing a breach in the airtight seal. This need for highly skilled workers to ensure that proper techniques are used during the chemical bonding process equates to higher training and more labor.
The use of chemical adhesives to bond the bladder material to the vent component also introduces an additional curing cycle to the overall coupling process which can increase the coupling time flow by as much as 40% or more compared to a coupling process that does not include the chemical adhesive curing cycle.
As discussed above, the results of the chemical bonding process can be inconsistent leading to failures in the airtight seal between the inflatable bladder and the vent component during testing and prior to use in composite fabrication. The impact on the time flow is multiplied when a chemical bonding process fails because the application and curing steps for the chemical bonding of the bladder and the vent component must be repeated before the elastomeric tool is used.
Additionally, the high pressures and high temperatures to which the adhesive bond of the elastomeric tool is exposed during the layup and curing processes during composite fabrication can increase the chance of failures. At best, a failure of the mold during the composite fabrication process can cause the loss of composite materials, time, revenue, and reputation. At worst, the improper functioning of the mold due to an undetected failure in the airtight chemical bond between the bladder material and the vent component can lead to structurally deficient components being integrated into a finished product.
The chemical adhesives themselves also represent added inconvenience and expense in terms of their acquisition, storage, handling, and disposal.
Accordingly, there is a need for a composite fabrication vent assembly that can be coupled to inflatable bladders used in composite manufacturing and does not suffer from the problems described above. The present invention satisfies these and other needs, and provides further related advantages.